Differences in Digestive Enzyme Activities, Microbial Diversity, and Gastrointestinal Fermentation in Red Abalone (Haliotis rufescens) and Pāua (Haliotis iris)

IntroductionAccurate sex determination is critical for spawning success in both conservation breeding programs and commercial aquaculture, yet non-invasive methods remain limited in abalone species. Traditional approaches rely on visual inspection, which requires substrate detachment, can cause injury, and may induce premature gamete release. Here, we present the first application of machine learning to automate sex classification in red abalone (Haliotis rufescens) using non-invasive ultrasound imaging technology.MethodsWe developed a labeled dataset of 246 high-quality ultrasound images from 44 individuals and benchmarked seven convolutional neural network architectures: VGG16, VGG19, ResNet50, ResNet101, YOLOv8, YOLOv11, and a custom convolutional neural network. Data partitioning by individual identity was essential to prevent artificially inflated accuracy from image leakage across splits.ResultsThe YOLOv8 architecture achieved the highest test accuracy of 85.7% (precision: 0.905 male, 0.816 female; recall: 0.845 male, 0.899 female), outperforming both classical architectures and custom models. Interestingly, a custom reverse VGG architecture with decreasing channel depth outperformed standard VGG models, suggesting that early channel compression may help combat ultrasound speckle noise.DiscussionFeature activation maps confirmed that models learned to attend to gonadal tissue rather than imaging artifacts. We also demonstrate inference on NVIDIA Jetson edge devices, enabling real-time classification suitable for field deployment. This framework establishes the feasibility of automated, non-lethal sex determination for mollusks and lays the groundwork for applications to endangered abalone species where traditional invasive methods are prohibited.

The presence of emerging contaminants (ECs) in South Africa’s marine coastal waters has received increasing attention, yet their ecotoxicological effects on indigenous species remain poorly understood. A major gap in monitoring is the absence of a standardised marine bioassay protocol. Although South Africa’s National Toxicity Monitoring Programme (NTMP) outlines water quality assessment for inland waters, it excludes marine ecosystems. In contrast, the United States Environmental Protection Agency (USEPA) recommends Haliotis rufescens for Whole Effluent Toxicity (WET) assessments. This study adapts the USEPA WET protocol for South African conditions by employing Haliotis midae, an economically important abalone species native to South Africa. A reference toxicant test with zinc sulphate was conducted, followed by exposures to five ECs commonly detected in South African coastal waters: Acetaminophen, Atrazine, Benzotriazole, Carbamazepine, and Emtricitabine. Toxicity tests at 100 µg/L, 50 µg/L, and 25 µg/L for each EC revealed significant developmental impairments at all concentrations, including the lowest tested. These effects occurred at levels comparable to reported environmental concentrations, underscoring H. midae’s high sensitivity to ECs. The bioassay met all USEPA acceptability criteria, confirming robustness, reproducibility, and environmental relevance. Zinc testing further validated H. midae as a suitable bioassay organism. This standardised, locally relevant assay offers a valuable tool for marine ecotoxicology in South Africa, with potential integration into national monitoring programmes. The work supports United Nations Sustainable Development Goals SDG 6 (Clean Water and Sanitation), SDG 14 (Life below Water), and SDG 15 (Life on Land) by advancing capabilities for monitoring and protecting aquatic ecosystems from emerging pollutants.

Diet-driven transcriptional changes in weaning red abalone (Haliotis rufescens) and its hybrid (H. rufescens [♀] x H. fulgens [♂]).

Marine gastropods support important artisanal, cultural, and commercial fisheries. However, overexploitation of abalone, conch, topshell, and limpets has resulted in population declines globally, with numerous species on the IUCN Red List of Threatened Species. Various efforts to supplement existing populations by either translocating wild or releasing hatchery-produced stock have suffered from low survival. To understand predictors influencing post-release survival, we conducted a systematic review and quantitative synthesis of literature on marine gastropod releases. Our global review identified 88 studies (575 unique release events) across 18 species. A similar number of releases were conducted in tropical (52 %) and temperate (48 %) regions, although most release events involved either Haliotidae (57 %) or Strombidae (26 %). Most releases used hatchery-produced stock (77 %), highlighting the prominent role of aquaculture. For seven species with sufficient data, we tested the effect of time since release, stock origin (hatchery, translocated), size at release, and density on post-release apparent survival (referred to as ‘survival’ hereafter), where applicable. Survival declined through time regardless of species. Hatchery-produced and translocated Haliotis fulgens had similar survival post-release, but hatchery-produced Aliger gigas had lower survival probability than translocated stock. Size at release increased survival probability for only two ( Haliotis discus and A. gigas) of the seven species. Similarly, density had no effect on the post-release survival of Haliotis rubra, Haliotis rufescens , and A. gigas . Overall, we found low long-term predicted survival across the seven species. Our findings highlight that overcoming low post-release survival is a significant hurdle when rehabilitating depleted stocks of marine gastropods. • Releasing stock is a key management strategy in recovering marine gastropods. • Understanding drivers of post-release survival will facilitate better outcomes. • Stock origin and size can influence post-release survival, but density does not. • For 7 gastropod species, we found poor long-term survival. • Population recovery through releases may not be a viable management strategy.

Los yacimientos en el oeste de la isla Santa Cruz, que datan entre 7000 y 5300 años, suelen contener llamativas conchas de abulón rojas, a pesar de que los fragmentos de conchas de mejillón son más abundantes. La mayoría de los yacimientos identificados al principio se encontraban en la costa o cerca de ella, pero en los últimos 30 años también se han documentado en lugares tierra adentro que ofrecen la oportunidad de aprender acerca del uso de los recursos alimentarios y la importancia de los recursos alimentarios costeros mientras se vive tierra adentro. Aunque, el muestreo a pequeña escala en algunos de los sitios tierra adentro se llevaron a cabo principalmente con el propósito de obtener muestras para la datación de radiocarbono, más recientemente se han excavado pozos de prueba a mayor escala en cuatro de ellos para obtener muestras lo suficientemente grandes como para evaluar cómo se articulaban los sitios con los sistemas de asentamiento. Los sitios que se encuentran tierra adentro de este período suelen presentar un área pequeña y están ubicados en una variedad de características topográficas. Algunos están enterrados bajo depósitos posteriores y otros pocos poseen estratos asociados que contienen conchas de abulón rojo. Los datos disponibles, aunque aún escasos, indican que pequeñas unidades sociales ocuparon sitios tierra adentro durante algunas semanas o meses seguidos, aparentemente para adquirir y consumir recursos alimenticios vegetales. Se necesitará mayores esfuerzos para localizar e investigar sitios tierra adentro durante el período 7000–5300 AP para crear una idea más clara.

Modulation of systemic antioxidant and immune responses in red abalone (Haliotis rufescens) during the recovery phase of anesthesia, in preparation for grafting surgery.

Modelling components of nacre structure in silico: Interactions of a nacre peptide with chitin and an aragonite surface.

Climate change and the associated shifts in species distributions and ecosystem functioning pose a significant challenge to the sustainability of marine fisheries and the human communities dependent upon them. In the California Current, as recent, rapid, and widespread changes have been observed across regional marine ecosystems, there is an urgent need to develop and implement adaptive and climate-ready fisheries management strategies. Climate Vulnerability Assessments (CVA) have been proposed as a first-line approach towards allocating limited resources and identifying those species and stocks most in need of further research and/or management intervention. Here we perform a CVA for 34 California state-managed fish and invertebrate species, following a methodology previously developed for and applied to federally managed species. We found Pacific herring, warty sea cucumber, and California spiny lobster to be three of the species expected to be the most sensitive to climate impacts with California halibut, Pacific bonito, and Pacific hagfish expected to be the least sensitive. When considering climate sensitivity in combination with environmental exposure in both Near (2030–2060) and Far (2070–2100) Exposure climate futures, red abalone was classified as a species with Very High climate vulnerability in both periods. Dungeness and Pacific herring shifted from High to Very High climate vulnerability and Pismo clam and pink shrimp shifted from Moderate to Very High climate vulnerability as exposure conditions progressed. In providing a relative and holistic comparison of the degree to which state-managed marine fishery species are likely to be impacted as climate change progresses, our results can help inform strategic planning initiatives and identify where gaps in scientific knowledge and management capacity may pose the greatest risk to California’s marine resource dependent economies and coastal communities.

Abstract Detrital subsidies such as leaf litter, animal carcasses, and marine wrack can profoundly shape recipient habitats by influencing resiliency and productivity. Species introductions and climate‐driven range shifts alter the quantity and quality of these subsidies in donor habitats, thereby potentially influencing recipient communities. Such impacts might be particularly important when detrital shifts alter detritivore feeding and performance. Attempts to identify a general theory predicting the consequences of invasive species on detritivores have been challenging, in part because most theories have been based on the study of microbes or consumers of living prey. Further, two recent meta‐analyses disagree about the impacts of invasive plants on detritivore populations. Here, we examined the potential impact of a human‐mediated shift in macroalgal detrital subsidy from native giant kelp (Macrocystis pyrifera) to invasive devilweed (Sargassum horneri) on recipient rocky shores, with an emphasis on exploring species‐specific impacts. We assessed consumer performance on single species diets or on a mixture in no‐choice assays, and we assessed feeding preference in choice assays. Additionally, we examined the impacts of this shift on grazing of native benthic seaweeds by an intertidal consumer assemblage. Replacing native Macrocystis with invasive Sargassum had consumer‐specific impacts on performance—suppressing growth of red abalone (Haliotis rufescens) but enhancing growth of black turban snails (Tegula funebralis). The effect of mixed diets on consumer growth also displayed consumer specificity. Also, replacing Macrocystis with invasive Sargassum increased grazing of native benthic seaweeds by a realistic detritivore assemblage, but only on the habitat‐forming brown seaweed, Silvetia compressa. Thus, invasion‐mediated changes in detrital wrack composition had consumer‐ and seaweed‐specific impacts. Such species specificity could underlie disagreements about the impact of species invasions on detritivore populations and could impede our ability to identify a general theory about how species invasions will impact recipient communities via detrital pathways.

Characterising patterns of genetic diversity including evidence of local adaptation is relevant for predicting and managing species recovering from overexploitation in the face of climate change. Red abalone (Haliotis rufescens) is a species of conservation concern due to recent declines from overharvesting, disease and climate change, resulting in the closure of commercial and recreational fisheries. Using whole-genome resequencing data from 23 populations spanning their entire range (southern Oregon, USA, to Baja California, MEX) we investigated patterns of population connectivity and genotype-environment associations that would reveal local adaptation across the mosaic of coastal environments that define the California Current System (CCS). We discovered high genetic diversity that is shared within and among populations, suggesting high historical range-wide gene flow. We found little evidence for large selective sweeps between populations that occupy local habitats that vary by pH, strength of upwelling, chlorophyll, salinity and sea surface temperature. This is consistent with a broad range of species with similar life histories that show limited neutral or adaptive genetic variation across the same region and the same environments, suggesting that the mosaic of environmental variation across the CCS is insufficient to drive local adaptation in the face of high gene flow for some broad-cast spawning species. Given the high genetic connectivity across their range, state-mandated regulatory actions would be most effective if aligned across jurisdictional boundaries (i.e., Mexico, California and Oregon).

Improved growth performance and physiological state in hybrid abalone (Haliotis rufescens and Haliotis fulgens) facing ocean acidification conditions

ABSTRACT Understanding the recruitment dynamics of invertebrates in kelp forests is critical to informing climate-ready restoration. Here we examine abalone and sea urchin recruitment (3–20 mm in size) patterns in northern California across a period of drastic change. Annual surveys were conducted before, during and after the MHW (2014–2016), the loss of a major predatory sea star (2012–2016) and the collapse of a bull kelp forest in 2014. Divers surveyed artificial reef recruitment modules (n = 12) over 20 years in an area that once supported dense bull kelp, Nereocystis leutkeana, forests and the world's largest recreational abalone fishery. From 2016 to 2022, we tracked the decline of red abalone, Haliotis rufescens, recruitment and the rise of purple sea urchin, Strongylocentrotus purpuratus, recruitment. Adult densities of purple sea urchins increased as did newly settled sea urchins (<3 mm), while adult and newly settled red abalone declined. Eight years after the kelp forest collapse, red abalone recruitment remained low and sea urchin recruitment continued to increase. Recruitment patterns can inform both abalone restoration targets and sea urchin dynamics as part of a more holistic kelp forest recovery plan that is responsive to climate change drivers.

Analysis of the presence of anti-viral innate immune pathways in the Australian Haliotis laevigata

The red abalone (Haliotis rufescens) represents North America’s most important aquaculture species. Its hepatopancreas is rich in cellulases and other polysaccharide-degrading enzymes, which provide it the remarkable ability to digest cellulose-rich macroalgae; nevertheless, its cellulolytic systems are poorly explored. This manuscript describes some functional and structural properties of an endogenous trimeric glycosylated endoglucanase from H. rufescens. The purified enzyme showed a molecular mass of 23.4 kDa determined by MALDI-TOF mass spectrometry, which behaved as a homotrimer in gel filtration chromatography and zymograms. According to the periodic acid-Schiff reagent staining, detecting sugar moieties in SDS-PAGE gel confirmed that abalone cellulase is a glycoprotein. Hydrolysis of cello-oligosaccharides and p-nitrophenyl-β-D-glucopyranosides confirmed its endo/exoactivity. A maximum enzyme activity toward 0.5% (w/v) carboxymethylcellulose of 53.9 ± 1.0 U/mg was achieved at 45°C and pH 6.0. We elucidated the abalone cellulase primary structure using proteases and mass spectrometry methods. Based on these results and using a bioinformatic approach, we identified the gene encoding this enzyme and deduced its full-length amino acid sequence; the mature protein comprised 177 residues with a calculated molecular mass of 19.1 kDa and, according to sequence similarity, it was classified into the glycosyl-hydrolase family 45 subfamily B. An AlphaFold theoretical model and docking simulations with cellopentaose confirmed that abalone cellulase is a β-sheet rich protein, as also observed by circular dichroism experiments, with conserved catalytic residues: Asp26, Asn109, and Asp134. Interestingly, the AlphaFold-Multimer analysis indicated a trimeric assembly for abalone cellulase, which supported our experimental findings. The discovery and characterization of these enzymes may contribute to developing efficient cellulose bioconversion processes for biofuels and sustainable bioproducts.

The structure and composition of mantle tissue from red abalone Haliotis rufescens were studied in relation to pearl farming. Histological (hematoxylin-eosin) and histochemical (PAS Alcian Blue, Sudan Black, Dahl's) tools were used to determine variations in the glycogen index, lipid index, and calcium coverage index of mantle tissue as a function of seasonality (cold and warm period) and body region (dorsal, central, ventral). Anatomically, only two well-developed and functional mantle folds (inner and outer) were observed across the marginal zone, together with a poorly developed, and presumably, rudimentary fold with the same cellular morphology as the inner fold. The inner mantle epithelium stored significantly higher concentrations of glycogen and mucins, triglycerides, and calcium than the outer epithelium. This pattern occurred significantly more during the cold season than during the warm season. Mucins from mantle tissue not only regulate crystal nucleation and orientation during biomineralization, but also give the inner nacreous layer its luster and color. High concentrations of lipids in mantle tissue could help compensate for the energy loss caused by the wound-healing processes associated with mantle tissue removal and seeding, which are stressful and energetically costly. The absorption of calcium ions from the environment to integrate a microlaminate of calcareous compounds gives the shell its structural properties of hardness and strength. An approach with molecular-ultrastructural tools is recommended to broaden the understanding of mantle tissue regionalization and its relationship to pearl sac formation, which may help increase pearl yield and quality in H. rufescens.

Changes in climate conditions can have cascading repercussions for organismal performance and survival, altering the productivity of aquatic systems. While numerous studies have examined the direct effects of temperature on species fitness, fewer studies have analyzed how individual impacts may translate to downstream primary consumers. Temperature-induced changes in the nutritional quality of seaweed may cause critical shifts in energy and nutrient availability for these consumers. A multifaceted experiment was conducted to assess the indirect impacts of California’s coastal climate conditions on abalone growth. This experiment fed juvenile red abalone (Haliotis rufescens) of two different size classes in ambient water conditions with the seaweed dulse (Devaleraea mollis), conditioned at 13°C, 15°C, and 17°C for 92 days. Nutritional analyses revealed significantly higher protein and nitrogen content in the 17°C dulse culture than in the 15°C and 13°C cultures, and no significant differences in carbohydrates. Furthermore, analyses on body weight ratio and condition factor indicate that juvenile red abalone of smaller size display significantly better growth and condition when fed dulse cultured at higher temperatures. Differences between size classes suggest that temperature changes, and subsequent shifts in the nutritional composition of dulse, may have greater impacts on smaller, younger red abalone.

ABSTRACT Co-culture of abalone and sea cucumber can result in benefits. This study investigated for 131 days the growth of juvenile red abalone (Haliotis rufescens) co-cultured with two densities of warty sea cucumbers (Apostichopus parvimensis). The initial mean (± SE) shell length of 1080 red abalone was 26.74 ± 1.04 mm, with a wet weight of 5.64 ± 0.12 g. The average weight of nine sea cucumbers was 175.26 ± 2.22 g. One experimental treatment had low density (LD) of sea cucumbers with a ratio of 1 gram of abalone to 0.25 grams of sea cucumber. The other, high density (HD) with a ratio of 1 gram of abalone to 0.50 grams of sea cucumber and a control treatment without sea cucumbers. There were no differences in abalone growth between treatments and the control; the only differences were among HD and LD. Abalone from the HD treatment had 19.40% higher growth than the control and 20.94% than the LD. Overall, the sea cucumbers in both treatments showed a decrease in body weight, 17.15% in the HD and 6.13% in the LD. We hope our results encourage further studies for developing multitrophic aquaculture in the Northeastern Pacific.

A fully assembled spirochaete genome was identified as a contaminating scaffold in our red abalone (Haliotis rufescens) genome assembly. In this paper, we describe the analysis of this bacterial genome. The assembled spirochaete genome is 3.25 Mb in size with 48.5 mol% G+C content. The proteomes of 38 species were compared with the spirochaete genome and it was discovered to form an independent branch within the family Spirochaetaceae on the phylogenetic tree. The comparison of 16S rRNA sequences and average nucleotide identity scores between the spirochaete genome with known species of different families in Spirochaetia indicate that it is an unknown species. Further, the percentage of conserved proteins compared to neighbouring taxa confirm that it does not belong to a known genus within Spirochaetaceae. We propose the name Candidatus Haliotispira prima gen. nov., sp. nov. based on its taxonomic placement and origin. We also tested for the presence of this species in different species of abalone and found that it is also present in white abalone (Haliotis sorenseni). In addition, we highlight the need for better classification of taxa within the class Spirochaetia.

Understanding the mechanisms by which individual organisms respond and populations adapt to global climate change is a critical challenge. The role of plasticity and acclimation, within and across generations, may be essential given the pace of change. We investigated plasticity across generations and life stages in response to ocean acidification (OA), which poses a growing threat to both wild populations and the sustainable aquaculture of shellfish. Most studies of OA on shellfish focus on acute effects, and less is known regarding the longer term carryover effects that may manifest within or across generations. We assessed these longer term effects in red abalone (Haliotis rufescens) using a multi-generational split-brood experiment. We spawned adults raised in ambient conditions to create offspring that we then exposed to high pCO2 (1180 μatm; simulating OA) or low pCO2 (450 μatm; control or ambient conditions) during the first 3 months of life. We then allowed these animals to reach maturity in ambient common garden conditions for 4 years before returning the adults into high or low pCO2 treatments for 11 months and measuring growth and reproductive potential. Early-life exposure to OA in the F1 generation decreased adult growth rate even after 5 years especially when abalone were re-exposed to OA as adults. Adult but not early-life exposure to OA negatively impacted fecundity. We then exposed the F2 offspring to high or low pCO2 treatments for the first 3 months of life in a fully factorial, split-brood design. We found negative transgenerational effects of parental OA exposure on survival and growth of F2 offspring, in addition to significant direct effects of OA on F2 survival. These results show that the negative impacts of OA can last within and across generations, but that buffering against OA conditions at critical life-history windows can mitigate these effects.